Etiology
In the majority of adult patients with preseptal cellulitis, the infection occurs from a superficial site of inoculation (e.g., insect bite, chalazion, epidermal inclusion cyst, folliculitis). In children, preseptal cellulitis may reflect an underlying sinusitis. In all ages, orbital cellulitis most often reflects local spread of an upper respiratory tract infection, usually sinusitis. Less common sources of orbital cellulitis are orbital injury, fracture, dacryocystitis, endophthalmitis ("panophthalmitis"), or underlying dental infections. More rarely, infection may spread hematogenously.[1][9][10][11][12][13] Organisms involved include Staphylococcus species, Streptococcus species, Haemophilus influenzae (in unimmunized individuals), and anaerobes.[14][15] Fungal infections (mucormycosis or invasive aspergillosis) have been seen in people with diabetic ketoacidosis or immunosuppression and recipients of organ transplantation, and are typically very aggressive and often fatal.
Pathophysiology
The bony orbit is thin, and is penetrated by many small nerves, vessels, and minute defects (Zuckerkandl dehiscences). This predisposes the area to the spread of infection from adjacent sinuses. Septic thrombophlebitis affecting the valveless veins that bridge the orbit and the sinuses also facilitate the spread of infection.[10][11] It is important to note that there are no lymphatics in the orbit that could serve as carriers of the infection from the sinuses to the orbit.
When sinusitis is the primary cause of periorbital or orbital cellulitis, infection usually spreads from the ethmoid sinuses across the thin lamina papyracea that separates the ethmoid sinus from the contents of the orbit. Less commonly, it spreads through the floor of the frontal sinus or the roof of the maxillary antrum.[12][13][16][17][18] Maxillary sinusitis often occurs secondary to an odontogenic source.
Eyelid edema in periorbital and orbital cellulitis results from obstructed venous and lymphatic drainage from the affected sinus. Signs and symptoms associated with orbital cellulitis (visual disturbance, reduced extraocular motility, chemosis, and proptosis) develop as a consequence of the inflammatory exudates extending into the orbit with soft tissue swelling resulting in increased orbital pressure.[10]
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